Hi Erik - I would recommend you try to have the current engine rebuilt, especially if it is the original one. Make sure to have it done by someone who knows what they are doing; places like Keizer as Peter recommends. But do shop around; some charge the moon (don't be surprised if you receive quotes in excess of EUR 12 thousand). When I needed to have my engine rebuilt in 2003, I learned quickly that most places will not tell you:
- what it is going to cost ("we'll need to open it up first Sir") - at that point, of course you are married without a prenuptial agreement
- how long it is going to take
- also, some have experienced troubles after the rebuild, so unless you are sure of the quality of the work ...
Other displacement engines of the Pagoda series will fit, but manual transmission engines will need to be modified somewhat to mate to your automatic transmission. Same with the sedan engines, and on those you need to fit the tachometer drive (no big deal, you should be able to just install the drive on your current engine).
In general, I would try to stay with the original displacement and would definitely not recommend fitting a totally different engine.
Check around on the forum, there's lots of information here. I do have a short block (lower part of the engine only) that was completely rebuilt, but it's for a 280 SL and without the head. Your 230 head would not fit. I have other 280 engines, whole and in parts, but none that are rebuilt.
One last option you should consider is having the work done farther away, by really specialised outfits (there is one in the UK and of course places like Metric Motors in the US - transporting an engine, if you use a good shipper, is less expensive than you might expect).
Good luck!
Cees